The present invention relates to a method of removing impurities from phosphate rock.
There are a variety of known techniques for removing impurities from solids, based on differences in characteristics between the pure solid and its impurities. For instance, materials can be separated based on their size, their density, their ability to hold an electrical charge, or their magnetic characteristics. These methods are useful for most solid separation applications, but there are some solids that cannot be economically separated by these methods because the pure solid and its impurities are too similar in these characteristics.
A solution to this problem is to use a different characteristic, such as affinity for water, to separate the solid from its impurities. In one known method, ash (a hydrophilic impurity) is separated from coal (a hydrophobic acid) by forming a coal slurry, mixing oil into the slurry to produce agglomerates, and recovering the agglomerates as product. Most of the ash remains in the aqueous phase of the slurry.
A major disadvantage of this method is that the oil used to agglomerate the coal becomes part of the product. This means that this process could not be used to separate other hydrophobic materials from their hydrophilic impurities whenever oil would not be a desirable part of the final product. It is possible to try to recover the oil from the agglomerates, but this would require extremely high temperatures (in excess of 260.degree. C.) and, even at these high temperatures, the oil recovery would not be complete.
It would be advantageous if a separation method could separate gangue minerals from phosphate rock by a process more energy efficient than the prior art processes. It would also be advantageous if a separation method could separate gangue materials from phosphate rock without agglomerates being in the final product.